Zea mays, commonly known as maize and corn, is a grain widely used in animal feed. The grain, i.e., kernel, is a source of protein, starch, and oil for swine, cattle, and poultry. Of the ten amino acids deemed essential in a mixed grain feed source, corn is particularly limiting in lysine, threonine, and methionine. The lack of these amino acids, especially lysine, requires that feed corn or corn meal be supplemented with these nutrients, often provided by the addition of soybean meal. It would be of benefit to the art to increase the level of lysine in corn kernel as a means of making the seed and meal more nutritious as an animal feed.
In order to increase levels of lysine using a molecular biological approach, a feedback-insensitive version of at least one of the lysine pathway enzymes, namely dihydrodipicolinic acid synthase (referred to herein as DHDPS), has been identified and employed. A bacterial DHDPS gene isolated from E. coli has been shown in vitro to be about 200-fold less sensitive to inhibition by increases in lysine levels and, when introduced into transgenic tobacco, over-expression of the E. coli DHDPS gene resulted in increased levels of lysine in leaf tissue (Glassman et al., U.S. Pat. No. 5,288,300). Falco et al. disclose transgenic plants with increased levels of lysine in the seed and genes useful for the production of such transgenic plants (U.S. Pat. Nos. 5,773,691 and 6,459,019; U.S. Patent Application Publication 2003/0056242, each of which is incorporated herein by reference in its entirety). In these reports, Falco et al. describe the isolation and use of feedback-insensitive DHDPS from E. coli and DHDPS from Corynebacterium (also known as cordapA) to generate transgenic rapeseed, tobacco, maize, and soybean plants with increased levels of lysine in the seed. For maize, Falco et al. report an approximately 130% increase in free lysine in kernels transformed with the cordapA gene relative to non-transformed kernels.
It would be advantageous to be able to detect the presence or absence of a particular transgene in a plant or seed, or progeny of such plants or seeds, not only with respect to the transgene itself, but also with respect to its location in the genome of a host plant or seed. Identification with respect to location further provides identification of the transgenic event by which a genetic engineer inserted the transgene into the progenitor plant of the plant or seed.